1. Field of the Invention
The present invention relates generally to a system for treating waste material in a molten state. More particularly, the present invention relates to a system for treating in a molten state waste material such as pulverized combustible material, e.g., dried sludge derived from sewerage, pulverized coal or the like material each including incombustible material in such a manner that the combustible material is burned, the incombustible material is molten in a swirling flow state in a combustion furnace installed in a inclined state with a horizontal attitude and then the molten slag is taken from the combustion furnace to the outside of the system. Further, the present invention relates a system for treating in a molten state fluid waste material such as dried sludge, pulverized coal, industrial waste liquid or the like material each including incombustible material in such a manner that the combustible material is burned, the incombustible material is molten in a combustion furnace, floatable dust carried by combustion waste gas to be discharged to the outside of the system is collected and molten in the high temperature atmosphere of a swirling flow in a dust removing unit installed in an inclined state with a horizontal attitude and the molten slag is collected and then taken from the combustion furnace to the outside of the system.
2. Statement of the Related Art
A swirling flow type combustion furnace which is constructed such that pulverized combustible material such as dried sludge, pulverized coal or the like material each including incombustible material is injected into the interior of the cylindrical combustion furnace together with combustion gas from the end wall or the side wall of the combustion furnace while generating an intense swirling flow, the incombustible material, i.e., combustion ash is molten under the influence of thermal energy derived from combustion and the molten slag is discharged through an outlet port of the combustion furnace has been hitherto known (refer to, e.g., an official gazette of Japanese Laid-Open Patent NO. 213408/1986 (hereinafter referred to as "Prior Invention 1") and a specification of Japanese Patent Application NO. 4489/1987 (hereinafter referred to as "Prior Invention 2").
A swirling flow type combustion furnace as disclosed in the Prior Invention 1 is constructed such that a cylindrical housing of the combustion furnace is installed in an inclined state by a predetermined inclination angle, a plurality of auxiliary burner each including a heavy oil feed pipe and a combustion air feed pipe are arranged on one end wall (end surface on the upstream side) of the combustion furnace, a cylindrical member including a waste gas outlet port on the upper side and a molten slag discharge port at the lower side is coupled to the other end wall (end surface on the downstream side) of the combustion furnace and a pulverized combustible material feed port and a combustion air inlet port are arranged at the upper part of the outer surface of the combustion furnace at positions in the vicinity of the end surface on the upstream side. Each of the auxiliary burners is designated in a concentrical doubled-layer structure comprising a heavy oil feed pipe and an air feed pipe, and a plurality of guide blades for generating a swirling flow are attached to the foremost end of each auxiliary burner.
On the other hand, the Prior Invention 2 discloses a swirling flow type combustion furnace installed in an inclined state with a horizontal attitude wherein the combustion furnace comprises a primary combustion furnace and a secondary combustion furnace. The secondary combustion furnace is formed with a combustion air feed port at an intermediate zone through which oxygen required for combustion can be introduced into the interior of the combustion furnace. In addition, the combustion furnace is provided with an orifice-shaped baffle plate so that a part of the interior of the combustion furnace upstream of the baffle plate is divided into three sections, i.e., an upstream zone, an intermediate zone and a downstream zone.
Further, a method and an apparatus for treating waste material in the form of fluid combustible material such as dried sludge, pulverized coal or the like material each including incombustible material by way of the steps of burning the waste material while generating an intense swirling flow along the inner wall surface of a combustion furnace in the presence of combustion air, melting the incombustible material and discharging the resultant molten slag to the outside of the combustion furnace have been hitherto known.
With the foregoing method and apparatus, floatable dust is generated in the swirling flow, while molten slag to be discharged out of the combustion furnace is deposited on the bottom of the combustion furnace. As the floatable dust is transferred to a subsequent step, it is transformed into a liquid phase, a solid phase or an intermediate phase including the both liquid and solid phases depending on a manner of variation of temperature in the apparatus and physical properties of components included in the waste material, e.g., a melting point and others.
Such floatable dust has a substantial effect on operations of essential units at a subsequent step, e.g., a heat exchanger, an electrical type dust collector or the like unit. The aforementioned behaviors have been already known.
When waste material is treated and incombustible material is molten, floatable dust to be discharged to the outside together with waste gas is generated under a condition that the waste gas flows at a high speed while swirling in the furnace atmosphere. Accordingly, it is required that a proper measure is taken such that the floatable dust is not transferred to the subsequent step. Otherwise, an operational load of various units in the waste gas processing system, e.g., a dry type electrical dust collector, a heat exchanger, a reheating boiler or the like unit is unavoidably increased at the subsequent step.
To remove floatable dust generated in a combustion furnace, it has been proposed that the floatable dust is caused to collide against a bath of molten slag, as disclosed in an official gazette of Japanese Laid-Open Patent NO. 70015/1988 (see FIG. 19).
However, this proposal has problems that a swirling flow in the combustion furnace is brought into a discharge passage 117 in which waste gas flows at a speed higher than that in the furnace and moreover the discharge passage 117 is opened above the surface of molten slag, whereby the floatable dust is unavoidably carried away directly into the discharge passage 117 without collision against the surface of molten slag.
Other proposal for removal of floatable dust produced in a combustion furnace in which waste material is burnt and incombustible material is molten is such that an inner diameter at the free-board section of a combustion furnace is determined as large as possible in order to correctly match with a low free descending speed of the floatable dust. However, it has been found that this proposal has a problem that the furnace is fabricated at an excessively high cost because of the increased inner diameter.
Another proposal is concerned with a cyclone as illustrated in FIG. 20. According to this proposal, floatable dust can be collected at the highest efficiency but it has been found that this proposal has still problems that gas duct is complicated in structure, the temperature on the wall surface of the cyclone is largely lowered as heat is radiated therefrom because the wall surface of the cyclone is designed very large compared with a quantity of waste gas to be discharged and moreover there tend to occur such malfunctions that floatable dust is adhered to the wall surface of the cyclone due to the foregoing reduced temperature and the housing of the cyclone is liable to clogged with the floatable dust in an extreme case.
It should be added that according to the aforementioned prior inventions, a floatable dust removal efficiency in the atmosphere at a high temperature is usually not in excess of 90%.